<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    
</body>
<script>
var score =parseFloat(prompt("请输入学生成绩"));
var grade =score
if(grade>=80){
    alert("学生成绩为A");
}else{
    alert("学生成绩为B");
}
</script>
</html>